The quality of Italian coffee is unstable, which may be caused by the temperature of coffee powder.

No barista will ignore the effect of "extraction temperature" on coffee, but few people realize that the extraction temperature is actually determined by "water temperature" and "coffee powder temperature".

In the daily operation, it is difficult for us to have the time and energy to accurately measure the temperature of coffee powder. However, it has become a consensus among baristas that excessive heat will cause the aroma of coffee powder to volatilize ahead of time. In addition, there are also many views that heat energy will cause coffee oil to seep to the surface and cause caking problems.

But these are the results of coffee powder overheating, in fact, the temperature of coffee powder itself will directly affect the extraction process and results.

The truth about the temperature of coffee powder

To explore the effect of coffee powder temperature, Dr Monika Fekete, from the Coffee Science Laboratory in Melbourne, Australia, conducted an in-depth study.

Under the quantitative conditions of carbon dioxide emissions, extraction water, extraction water temperature and coffee cup temperature, Dr. Fekete conducted grouping experiments on coffee powders that were ground and mixed several times and stored at-13 °C, 8 °C, 21 °C, 45 °C and 55 °C, respectively.

The experimental results show that the temperature of coffee powder has no significant effect on coffee liquid weight, extraction rate and TDS, but has a positive correlation with coffee liquid temperature. With the increase of the temperature of coffee powder, the temperature of the final coffee liquid also increases, and vice versa.

The really interesting flow rate is non-linearly related to the temperature of coffee powder.

The flow velocity decreases with the increase of temperature from-13 °C to 8 °C, increases with the increase of temperature from 8 °C to 45 ℃, and decreases with the increase of temperature from 45 °C to 55 °C.

As a result of further experiments, the doctor finally confirmed that the viscosity of the coffee liquid was the main reason that affected the flow rate.

The lower the viscosity of coffee liquid is, the faster the flow rate is, and the increase of temperature can effectively reduce the viscosity of coffee liquid, which explains why the thickness of Italian concentrated alcohol is more obvious at low temperature.

Chain reaction of temperature

In daily operation, the temperature of ground coffee powder is about 10 ℃ higher than that of cooked beans. On the other hand, the temperature changes in the grinding environment, such as the rotational speed of the cutter head and continuous working hours, make the coffee powder constantly change between 25 °C and 50 °C.

The obvious time for this change is the peak period of visitors. During the peak period, the flow rate of Italian concentration will also be significantly accelerated. When the peak is over, the flow rate will gradually return to the state of dial-in in the morning.

Sometimes in order to solve the situation of excessive extraction, baristas have to temporarily adjust the grinding scale to make up for it, but the changes in the solubility of compounds at different temperatures have had an irreversible effect on the product.

And this is just one of a series of chain reactions. When the bean grinder begins to heat up, the diameter distribution of coffee powder will change, and those traditional quantitative bean grinders that use volume, timing and other methods will even produce changes in powder quantity, which greatly reduces the stability of the product.